The invention relates generally to current monitoring and, more particularly, to monitoring currents leaking between high voltage sources and ground.
In power switching stations, the quality of insulators and high voltage isolation devices is of central importance. Monitoring leakage currents during operation could provide information on the quality of high voltage insulators and changes in the quality due to age.
Monitoring weak leakage currents inside an operating high voltage power station is difficult for several reasons. A power station is a source of both electromagnetic (EM) noise and high fluctuating currents. For example, power stations employ radio transmitters to relay control and/or data signals. These transmitters produce radio frequency backgrounds that can mask signals from weak currents. Power switching operations also produce EM backgrounds, which mask weak signals and can damage sensitive amplifiers. Nearby lightning strikes can produce high leakage currents from insulators in the station, e.g., up to about 60,000 amps. Such currents can damage sensitive monitoring equipment. Varying temperatures can introduce systematic errors into current monitoring measurements performed at an outdoor power station. EM noise, high currents and temperature variations can interfere with the monitoring of leakage currents in a power station.
It is an important object of the invention to provide improved current monitoring.
In a first aspect, the invention provides a device for monitoring leakage currents between insulators for high voltage conductors and ground. The device includes a transformer and an amplifier. The transformer comprises a primary wire and a secondary winding. The primary wire carries a leakage current from the insulator to the ground. The amplifier has two input terminals connected across the secondary winding and produces an output signal proportional to the leakage current.
In a second aspect, the invention provides a device for monitoring leakage currents between a high voltage insulator and ground. The device includes a transformer and an amplifier. The transformer has a primary wire and a secondary winding having a resistance. The primary winding is adapted to carry a leakage current from the high voltage insulator to ground. The amplifier has input terminals connected across the secondary winding. The amplifier produces a voltage rise across the secondary winding substantially cancelling a voltage drop caused by the resistance. The amplifier produces an output signal responsive to a current in the secondary winding.
In a third aspect, the invention provides a method of monitoring leakage currents from insulators for high voltage conductors. The method includes producing a leakage current in a grounding wire attached to the insulator and producing a current in a winding inductively from the leakage current in the grounding wire. The method also includes applying a voltage across the winding to cancel a voltage drop in the winding due to the winding resistance and measuring the inductively produced current.
In a fourth aspect, the invention provides a device for monitoring leakage currents from a high voltage insulator. The device includes a grounding wire electrically connecting the high voltage insulator to ground and a metal housing having a hole. The grounding wire passes through the hole. The device also includes an amplifier, a magnetically permeable core, and a secondary winding, all located in the housing. The core inductively couples the secondary winding to the grounding wire, which passes through the core. The secondary winding attaches across first and second input terminals of the amplifier.